The long range objective of this work is to develop a sensitive in vitro assay system, which can be performed within 6 hours, can detect and/or distinguish in potential transplant recipients between cytotoxic and enhancing antibodies directed against a specific donor, and has high reliability for clinical use. With these objectives in mind, we have developed two antibody-dependent cell mediated cytotoxicity (CMC) assays to measure the presence of antibody in prospective kidney recipients. Preliminary results suggest that these assays are several times more sensitive than the complement dependent lymphocytotoxicity assay currently employed in cross match tests. The antibody dependent CMC assay will be performed on all cadaver and live donor-recipient pairs in our clinical transplant program. We will correlate the results of these assays with kidney graft rejection and the two other types of cytotoxic assays (complement dependent and pure CMC) which have been suggested as methods to measure presensitization. The nature, cytotoxic or enhancing, of the CMC assays will also be investigated. Because of the time required to evaluate clinical transplants in man, we will use the dog as a model to study the system. Finally, since our data indicates that two types of antibody-dependent CMC mechanisms are operative in these patients, we propose to determine the mechanisms by which they function, including the immunoglobulin class to which the antibodies belong, the requirement of the Fc fragment and their relationship to enhancing antibody as detected by the inhibition of the mixed lymphocyte culture reaction.